OK , I’ll bite. Good book, but how is it genre-defining?
It's habitually a Top 10 book on Locus, and won both the Hugo and Nebula its year.
Narratively, it showed a conceivable future that readers could imagine. It showcased harsh, grounded societies (i.e.. NOT Niven or Asimov), with realpolitik mindsets (NOT Delaney or Clarke) and hard sci-fi realities (NOT Cordwainer, or honestly any other giant on this list), and did it without psychedelics (Lookin' at you, Philip K) or by lightly reskinning WW2 archetypes (Bradbury, Vonnegut). It reads more like Orwell's 1984 than it does anything Niven/Asimov/Delaney/Smith/etc. were putting out.
It's one of the earliest sci-fi books with a realistic, Bechdel-test-passing female character. Wyoh has a backstory beyond her relationship to a man (mom/wife/daughter), she has agency and she does more than incite the male protagonist to action. I'm not sure Asimov ever had one.
To my knowledge, it was also the first time anyone wrote about using a gravity well as a weapon, and that has since been used by a multitude of other series -- notably, the Expanse, quite recently.
Not putting down Niven, Asimov, Delaney, Dick, Clarke, Bradbury or Vonnegut--they're great! But Moon is a statement piece defining hard, grounded scifi for easily a generation of writers.
I'd put it up next to Neuromancer, Cryptomonicon, Hyperion, Foundation, 451, Scanner, etc. as a defining works in the field.
